Traditional captioning devices, such as televisions and display monitors, combine text with a video broadcast, in which the text represents a transcribed audio portion of the video. The captions can be either closed captions or open captions. For closed captions, the caption data is embedded in a video signal, and the captions are not displayed unless they are decoded. The text or caption data is embedded in line 21 of the vertical blanking interval (VBI). The VBI is an interval in a television signal that temporarily suspends transmission of the signal for an electron gun to move to the first line of a television screen for the next screen field. The VBI can be used to carry data, such as a test signal or the closed-captioning data. When captions are decoded, they are displayed on the screen. Typically, captions are decoded at the display device. Open captions are already decoded in the video signal and are displayed on screen, such as subtitles in foreign films. In broadcast transmission systems, caption data may be transmitted to an encoder that may include text and control codes.
Caption data may also be provided to the internet using transcribed data from broadcast sources, such as broadcast radio or television signals. For instance, a caption writer for a radio station may transcribe a broadcast program from the radio station to post on the radio station's web page. In another example, a caption writer may caption the audio portion of a television signal and send the caption data to an encoder device at a broadcast facility for inclusion in the video transmission.